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R u I e S 0 f T hum h square shows the edge of the board to be square to the surface, but the square cannot reveal a twist in the surface. This can only be revealed on a flat surface or by using a pair of winding sticks. Mortise-and-tenon joints There are numerous ways a mortise-andtenon joint can be affected when the lumber is not prepared correctly. For example, when you assemble a table frame and dryfit the legs to one rail, one or both legs angle inward or outward and are not parallel. Track down the problem, disassemble the legs from the rail and check that the shoulder is square to the edge of the board. Splay can be introduced into a leg by the end of the rail not being square. A lot of people cut a board to length and assume that it is square. They then use the end of the board as a reference to scribe the shoulder lines using a marking gauge, or using this end against the fence or the table if cutting the tenons on the tablesaw. The unsquare end will be transmitted into unsquare shoulders, which in turn will introduce splay or twist into the leg. The solution is to use a square to check the ends of the boards. If the end of the rail is square, examine the straightness of the rail's edge. Check the one you placed the head of the square against when laying out the shoulders. Use a long straightedge or place the board on a machine tabletop. A curved edge will introduce an angle into the shoulder. If the lower edge of the rail is convex, the legs will splay; if it is concave, the legs will an- A PROBLEM DRAWER (conti nued) MORTISE-AND-TENON PROBLEMS Not all flared legs are intentional. Poorly prepared stock can leave legs canted in and out. SPREADING LEGS Bowed rail The board ends can be square, but failure to check the whole edge for straightness can result in legs that splay. TWIST THOSE LEGS Twisted side rail The tenon can be perfectly square to the board, but if the board is twisted over its length, the result will be twisted legs. gle inward. The reverse is Ul.le when testing the top edge. Another common problem is a mortised and tenoned face frame that doesn't lie flat. After taking apan the joint, make sure the tenon is parallel to the surface of the board. If it checks out fine, you then need to test the rail for flatness. If you find the reference surface has a twist, you transfer Right angle, wrong tool. A combination square can tell you if a board's edge is exactly 900 to its adjacent sides, but it will not be able to detect twist in a board. this twist into the tenon because you are working off an imperfect surface. Dovetailed drawers Frustration can mount when you assemble a drawer and find a space in the end of the dovetails, or when you have a drawer box that is twisted and doesn't sit flat. As with previous joint problems, the faults can be traced back to the improper preparation of the lumber. A gap at the end of the dovetail is most likely created by the end of the board not being square. If the overall edge of a drawer side is concave or convex, the drawer box will twist when assembled. Once again, check the overall straightness of the edge before cutting the joint. The other way in which a twist can occur If the end of the board is not square to the edge, one or more corners of an assembled drawer will not sit flat. 92 F r NE W 0 0 D W 0 R KIN G is when the drawer side is planed with a twist in the surface. This always puts the drawer front and back in wind to one another. Once the drawer has been assembled, planing material from the bottom edge of one side in turn makes the drawer front tilt; if enough material is removed from both sides of the drawer, the bottom can rub on d1e frame. 0 Square but not straight. A combination square will show you that the end is square to the board's edge. It will not reveal whether the edge is flat over its entire length.